iPhone 6 Plus boot white apple restart repair

Machine model: iPhone 6 Plus
Malfunction: Stuck on Apple logo restarts after startup.
Maintenance process: the startup current of DC power supply switch starts at 200mA, and it becomes stop at Fixed current 300mA after normal current of change to 1A.

iPhone 6 Plus boot white apple restart repair Figure 1.

This situation is mostly caused by USB problems, and it is found that it is not online in Recovery mode.

iPhone 6 Plus boot white apple restart repair Figure 2.

The USB chip is removed and powered on again. The current of switch is still 200MA. It seems that it is not the USB chip itself.

multimeterdiode; the one who lacks dialectical thinkin gMeasure the ground value of VCC near USB, and find the PP3V0 _ tristar/PAC _ VDD _ 3V0 shorted to ground of USB.

Through Boardview, it is found that VCC is the main power supply, which passes through USB,fingerprint boost chip and U5411_RF, and it is unlikely that the power supply will be damaged in the past experience.

Remove the fingerprint boost chip, and the power-on fault remains the same. Since it is still the case, remove U5411_RF, because PP3V0_TRISTAR/PAC_VDD_3V0 is sent to U5411_RF VCC through L5408_RF. Remove L5408_RF, turn on switch, and find that the jump is normal. Reinstall the USB mobile phone and start it normally.